Squarylium compounds and optical recording media using the same

ABSTRACT

An object of the present invention is to provide novel squarylium compounds having the spectroscopic properties, light resistance, solubility and thermal decomposition properties suitable for a recording material for DVD-R, and optical recording media using the same. More particularly, the present invention provides novel squarylium compounds represented by the general formula (I). In addition, the present invention provides optical recording media having a recording layer containing said squarylium compound.

TECHNICAL FIELD

[0001] The present invention relates to novel squarylium compounds whichcan be used in the optical recording field, and to optical recordingmedia using the same.

BACKGROUND ART

[0002] In recent years, development of a digital versatiledisc-recordable (DVD-R) as a recordable optical recording medium havinga higher recording density than that of a compact disc-recordable (CD-R)has been under going. Both of CD-R and DVD-R are similar to each otherin that an organic dye is utilized therein as a recording material andin a principle of recording and reproducing of a signal (information).Therefore, the organic dyes developed for CD-R can basically comply withthe various requirements (light resistance, solubility, thermaldecomposition properties) for the recording material of DVD-R other thanspectroscopic properties. However, an oscillation wavelength of asemiconductor laser, which is used for recording the signal to DVD-R orfor reproducing the signal from DVD-R, is in the range of 600-700 nm,which is shorter than that of the semiconductor laser which is used forCD-R Accordingly, the recording material utilized for DVD-R should havean absorbance end of a longer wavelength side shorter than that of CD-Rwhen it exists in the form of a membrane. Therefore, the dyes developedfor CD-R such as cyanine dyes, azzaannulene dyes and indoaniline-metalchelate dyes (“Electronics Related Dyes”, CMC, 1998) can not be used asthe recording material for DVD-R

[0003] The present inventors have developed squarylium compounds havingdifferent two kinds of aromatic substituents in a molecule. Suchsquarylium compounds have a squaric acid skeleton at a center of themolecule and substituents comprising an aromatic compound on carbonatoms at two catercornered positions of the skeleton. Squaryliumcompounds having two same aromatic substituents are convenientlyreferred to as symmetric squarylium compounds (or symmetric squaryliumdyes), whereas those having different two kinds of substituents arereferred to as asymmetric squarylium compounds (or asymmetric squaryliumdyes).

[0004] The asymmetric squarylium compound having as a substituent anaromatic ring bound to a squaric acid skeleton with a carbon atom of thearomatic ring and an aromatic amine bound to the squaric acid skeletonwith an amino group has been previously known (Japanese UnexaminedPatent Publication No. 92914/1994). OXOCARBONS (Academic Press, 1980)describes a compound in which an aromatic substituent bound to thesquaric acid skeleton with a carbon atom is phenyl. However, since thecolor of these compounds is yellow, brown or red, it is believed thatthe maximum absorption wavelength of these compounds is 500 nm orshorter and, therefore, these compounds can be scarcely used as arecording material for DVD-R from a viewpoint of the spectroscopicproperties.

[0005] In addition, Japanese Unexamined Patent Publication No.92914/1994 describes a compound in which an aromatic substituent boundto the squaric acid skeleton with a carbon atom is an azulenyl group.However, the molar extinction coefficient of such a compound is 4.8 orsmaller and, therefore, the compound is unsuitable for the recordingmaterial for DVD-R from a viewpoint of the spectroscopic properties.

[0006] In view of an oscillation wavelength of the semiconductor laserused for DVD-R, for spectroscopic properties of the recording material,which have the close relation with recording and reproducingsensitivities of the signal, it is desirable that the maximum absorptionwavelength (λ_(max)) of the recording material measured in its solutionis within the range of 550-600 nm and log ε thereat (ε is a molarextinction coefficient) is 5 or greater. In addition, for thermaldecomposition properties of the recording material, which have the closerelation with the recording sensitivity, it is desirable that asignificant loss in weight is observed within the temperature range of250-350° C.

[0007] Furthermore, although light resistance and solubility in asolvent which is necessary for membrane formation are also required asthe property of the recording material, there is no recording materialhaving suitable properties for DVD-R, such as spectroscopic properties,light resistance, solubility and thermal decomposition properties, inthe known squarylium compounds.

DISCLOSURE OF THE INVENTION

[0008] An object of the present invention is to provide squaryliumcompounds having spectroscopic properties, light resistance, solubilityand thermal decomposition properties suitable as a recording materialfor DVD-R, and optical recording media using the same.

[0009] The present invention was done based on such a finding, andprovides squarylium compounds represented by the formula (I):

[0010] wherein, R¹ and R² are the same or different, and represent ahydrogen atom, an alkyl group optionally having a substituent, anaralkyl group optionally having a substituent, an aryl group optionallyhaving a substituent or a heterocyclic group optionally having asubstituent, or R¹ and R² may be taken together with an adjacentnitrogen atom to form a heterocycle, wherein the heterocycle may have asubstituent, and R³ represents the general formula (II):

[0011] wherein, R⁴ and R⁵ are the same or different, and represent ahydrogen atom or an alkyl group, or R⁴ and R⁵ may be taken together withan adjacent nitrogen atom to form a heterocycle, and R⁶, R⁷, R⁸ and R⁹are the same or different, and represent a hydrogen atom, an alkyl groupoptionally having a substituent, an alkoxy group optionally having asubstituent, a hydroxyl group or a halogen atom, or R⁴ and R⁶ or R⁵ andR⁷ may be taken together with adjacent N—C—C to form a heterocycle,wherein the heterocycle may have a substituent; or the general formula(III):

[0012] wherein, R¹⁰ represents a carbon or nitrogen atom, R¹¹ and R¹²are the same or different, and represent a hydrogen atom, an alkyl groupoptionally having a substituent, an aryl group optionally having asubstituent, an aralkyl group optionally having a substituent, or ahydroxyl group (provided that, when R¹⁰ is a nitrogen atom, then R¹² isnot present), R¹³ represents a hydrogen atom, an alkyl group optionallyhaving a substituent, an aryl group optionally having a substituent oran aralkyl group optionally having a substituent, and R¹⁴ and R¹⁵ arethe same or different, and represent a hydrogen atom, an alkyl groupoptionally having a substituent, an alkoxy group or a halogen atom, orR¹⁴ and R¹⁵ may be taken together with two adjacent carbon atoms to forman alicyclic hydrocarbon group, an aromatic ring optionally having asubstituent or a heterocycle optionally having a substituent.

[0013] Also, the present invention provides optical recording mediahaving a recording layer comprising said squarylium compound.

BRIEF DESCRIPTION OF DRAWING

[0014] Description of Drawing

[0015]FIG. 1 is a graph illustrating a typical thermogravimetric curve(heating speed of 10° C./min.) for the squarylium compound of thepresent invention.

[0016] Description of Symbols

[0017] T1: Weight losing-initiation temperature,

[0018] T2: Weight losing-termination temperature,

[0019] M0: Initial weight,

[0020] m1: Ratio of remaining weight at T1, and

[0021] m2: Ratio of remaining weight at T2.

BEST MODE FOR CARRYING OUT THE INVENTION

[0022] Detailed Description of the Invention

[0023] The present invention will be illustrated below, and herein thecompound represented by the formula (I) is referred to as a compound(I). This is also applicable to compounds with the other formula numbersadded.

[0024] First, in the definitions of substituents in the above formula(1), an alkyl part of the alkyl and alkoxy groups includes straight orbranched alkyl groups having from 1 to 6 carbon atoms and cyclic alkylgroups having from 3 to 8 carbon atoms, such as methyl, ethyl, propyl,iso-propyl, butyl, iso-butyl, sec-butyl, tert-butyl, pentyl, iso-pentyl,1-methylbutyl, 2-methylbutyl, tert-pentyl, hexyl, cyclopropyl,cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl groups,and the like.

[0025] An aryl part of the aryl or aralkyl group includes, for example,phenyl, naphthyl and anthryl groups, and the like.

[0026] Examples of the aralkyl group include aralkyl groups having from7 to 15 carbon atoms, such as benzyl, phenethyl, phenylpropyl andnaphthylmethyl groups, and the like.

[0027] The halogen atom includes each atom of fluorine, chlorine,bromine, and iodine.

[0028] The heterocycle in the heterocyclic group or the heterocyclewhich is formed by R¹⁴ and R¹⁵ being taken together with two adjacentcarbon atoms includes aromatic heterocycles and alicyclic heterocycles.

[0029] Examples of the aromatic heterocycle include 5- or 6-memberedmonocyclic aromatic heterocycles containing at least one atom selectedfrom nitrogen, oxygen and sulfur atoms, fused di- or tri-cyclic aromaticheterocycles, which are formed by fusing 3-to 8-membered rings and whichcontain at least one atom selected from nitrogen, oxygen and sulfuratoms, and the like, and, more particularly, include pyridine, pyrazine,pyrimidine, pyridazine, quinoline, isoquinoline, phthalazine,quinazoline, quinoxaline, naphthyridine, cinnoline, pyrrole, pyrazole,imidazole, triazole, tetrazole, thiophene, furan, thiazole, oxazole,indole, isoindole, indazole, benzimidazole, benzotriazole,benzothiazole, benzoxazole, purine and carbazole rings, and the like.

[0030] In addition, examples of the alicyclic heterocycle include 5- or6-membered mono-alicyclic heterocycles containing at least one atomselected from nitrogen, oxygen and sulfur atoms, and fused di- ortri-alicyclic heterocycles, which are formed by fusing 3- to 8-memberedrings and which contain at least one atom selected from nitrogen, oxygenand sulfur atoms, and the like, and, more particularly, includepyrrolidine, piperidine, piperazine, morpholine, thiomorpholine,homopiperidine, homopiperazine, tetrahydropyridine, tetrahydroquinoline,tetrahydroisoquinoline, tetrahydrofuran, tetrahydropyran,dihydrobenzofuran and tetrahydrocarbazole rings, and the like.

[0031] Examples of the heterocycle which is formed by R¹ and R² or R⁴and R⁵ being taken together with an adjacent nitrogen atom, or formed byR⁴ and R⁶ or R⁵ and R⁷ being taken together with adjacent N—C—C includean aromatic heterocycle containing a nitrogen atom and an alicyclicheterocycle containing a nitrogen atom.

[0032] Examples of the aromatic heterocycle containing a nitrogen atominclude 5- or 6-membered monocyclic aromatic heterocycles containing atleast one nitrogen atom, fused di- or tri-cyclic aromatic heterocyclescontaining at least one nitrogen atom, which are formed by fusing 3- to8-membered rings, and the like, and more particularly include pyridine,pyrazine, pyrimidine, pyridazine, quinoline, isoquinoline, phthalazine,quinazoline, quinoxaline, naphthyridine, cinnoline, pyrrole, pyrazole,imidazole, triazole, tetrazole, thiazole, oxazole, indole, isoindole,indazole, benzimidazole, benzotriazole, benzothiazole, benzoxazole,purine and carbazole rings, and the like.

[0033] In addition, examples of the alicyclic heterocycle containing anitrogen atom include 5- or 6-membered monocyclic alicyclic heterocyclescontaining at least one nitrogen atom, fused di- or tri-cyclic alicyclicheterocycles containing at least one nitrogen atom, which are formed byfusing 3- to 8-membered rings, and the like and, more particularly,include pyrrolidine, piperidine, piperazine, morpholine, thiomorpholine,homopiperidine, homopiperazine, tetrahydropyridine, tetrahydroquinoline,tetrahydroisoquinoline, tetrahydropyran and tetrahydrocarbazole rings,and the like.

[0034] Examples of the alicyclic hydrocarbon ring which is formed by R¹⁴and R¹⁵ being taken together with two adjacent carbon atoms includesaturated or unsaturated alicyclic hydrocarbons having from 3 to 8carbon atoms, such as cyclopropane, cyclobutane, cyclopentane,cyclohexane, cycloheptane, cyclooctane, cyclopentene,1,3-cyclopentadiene, cyclohexene and cyclohexadiene rings, and the like.

[0035] Examples of the aromatic ring which is formed by R¹⁴ and R¹⁵being taken together with two adjacent carbon atoms include aromaticrings having from 6 to 14 carbon atoms, such as benzene, naphthalene andanthracene rings, and the like.

[0036] Examples of the substituents for the aryl group, an aralkylgroup, a heterocyclic group, aromatic ring, heterocycle containing anitrogen atom or heterocycle are the same or different 1-5 substituents,such as a hydroxyl group, a carboxyl group, a nitro group, an alkoxygroup, an alkyl group, an aralkyl group, a cyano group, a halogen atom,—R¹⁶═R¹⁷—Ar (wherein, R¹⁶ and R¹⁷ are the same and represent N or CIH,and Ar represents an aryl group optionally having a substituent selectedfrom the group consisting of a hydroxyl group, a carboxyl group, a nitrogroup, an alkoxy group, an alkyl group optionally substituted with ahalogen group, a cyano group and a halogen atom), and the like. Thealkyl group, alkoxy group, aralkyl group, aryl group, and halogen atomhave the same meanings as defined above.

[0037] Examples of the substituents for the alkyl group or alkoxy groupare the same or different 1-3 substituents, such as a hydroxyl group, acarboxyl group, a nitro group, an alkoxy group, an aryl group, and ahalogen atom, and the like. The alkoxy group, aralkyl group, aryl groupand halogen atom have the same meanings as defined above.

[0038] Among the squarylium compounds represented by the general formula(I), preferable compounds are (1) squarylium compounds in which R¹ andR² in the formula are taken together with an adjacent nitrogen atom toform a carbazole ring optionally having a substituent, or (2) squaryliumcompounds in which R¹ in the general formula (I) is a hydrogen atom, andR² is an aryl group substituted with —R¹⁶═R¹⁷—Ar (R¹⁶, R¹⁷ and Ar havethe same meanings as defined above). Moreover, among the compounds (1)and (2) as described above, squarylium compounds in which R³ is a grouprepresented by the general formula (III) are more preferable.

[0039] Next, a general method for preparing the compound (I) will beillustrated below.

[0040] The compound (I) can be prepared by, for example, reacting3,4-dichlorobutene-1,2-dione with an aromatic compound, containing anitrogen atom, which bonds to the squaric acid skeleton at a carbon atomor an aromatic amine which bonds to the squaric acid skeleton at anamino group in a solvent which does not inhibit the reaction, if needed,in the presence of a base, followed by hydrolysis, and reacting underheating the product and an aromatic amine which bonds to the squaricacid skeleton at an amino group or an aromatic compound, containing anitrogen atom, which bonds to the squaric acid skeleton at a carbon atomin a solvent.

[0041] The reaction can be represented by the following Schemes.

[0042] wherein R¹, R² and R³ have the same meanings as defined above,and Y represents a halogen atom such as chlorine or bromine, or OR¹⁶(R¹⁶ represents an alkyl group), wherein the alkyl group has the samemeanings as defined above.

[0043] Scheme (1-a)

[0044] The compound (IV) is prepared by reacting the compound (II) with0.4- to 2-fold mole of the compound (III) in a solvent, if needed, inthe presence of 0.4- to 2-fold mole of a base, at 0° C. to roomtemperature for 1-4 hours.

[0045] Examples of the base include organic bases such as quinoline,triethylamine, pyridine, and the like, and inorganic bases such aspotassium carbonate, potassium hydrogen carbonate, sodium hydrogencarbonate, and the like.

[0046] Examples of the solvent include chloroform, dichloromethane and1,2-dichloroethane, ethyl acetate, diethyl ether, methyl-t-butyl ether,tetrahydrofuran, toluene, benzene, dimethylformamide, dimethyl sulfoxideand the like.

[0047] (Scheme 1-b)

[0048] The compound (V) is prepared by reacting the compound (IV) in a50-90 volume/volume % aqueous solution of acetic acid at 90-110° C. for1-7 hours, or in 50-99% by weight of an aqueous solution oftrifluoroacetic acid or concentrated sulfuric acid at 40-60° C. for 1-3hours.

[0049] Scheme (1-c)

[0050] The compound (I) is prepared by reacting the compound (V) with0.5- to 2-fold mole of the compound (VI) if needed, in the presence of abase, at 80-120° C. for 1-15 hours.

[0051] Examples of the solvent to be used include only alcoholicsolvents having from 2 to 8 carbon atoms such as ethanol, propanol,iso-propanol, butanol, octanol, and the like, and a mixture of thealcoholic solvent and benzene or toluene (50 volume/volume % or more ofalcohol is contained).

[0052] Examples of the base to be used include organic bases such asquinoline, triethylamine, pyridine, and the like, and inorganic basessuch as potassium carbonate, potassium hydrogen carbonate, sodiumhydrogen carbonate, and the like. An amount of the base to be used ispreferably 1.0-2.0 equivalents, and more preferably 1.0-1.2 equivalentsrelative to the compound (V).

[0053] Scheme (2-a)

[0054] The compound (VII) can be prepared according to a manner similarto that described in Scheme (1-a) except that the compound (VI) is usedinstead of the compound (III).

[0055] Scheme (2-b)

[0056] The compound (VII) can be prepared according to a manner similarto that described in Scheme (1-b) except that the compound (VII) is usedinstead of the compound (IV)

[0057] Scheme (2-c)

[0058] The compound (I) can be prepared according to a manner similar tothat described in Scheme (1-c) except that the compound (VIII) is usedinstead of the compound (V) and the compound (III) was used instead ofthe compound (VI).

[0059] After the reaction, the compound (I) is purified and isolated,for example, by conducting distillation of a solvent or filtration, andif needed, by further purification with procedures conventionallyutilized in the synthetic organic chemistry (column chromatography,recrystallization, washing with a solvent, or the like).

[0060] Embodiments of the compound (I) are shown in Tables 1-3. CompoundNos. in the tables correspond to the Example numbers as described below.In addition, in the tables, Me represents a methyl group, Et representsan ethyl group, and ^(n)Bu represents a n-butyl group. TABLE 1Embodiments of squarylium compound (I) Examples R³—

1

2

3

4

5

6

7

[0061] TABLE 2 Embodiments of squarylium compound (I) Examples R³—

 8

 9

10

11

12

13

14

15

16

[0062] TABLE 3 Embodiments of squarylium compound (I) Ex- amples  R³—

17

18

19

20

[0063] Next, the constitution of a recording medium utilizing thesquarylium compound of the present invention (hereinafter, it may bereferred to as “a compound of the present invention”) will beillustrated.

[0064] The physical properties required for a material for a recordinglayer include optical and thermal properties. The optical properties arepreferably such that there is a large absorption band at a shorterwavelength side than 600-700 nm, preferably 630-690 nm, which is arecording or reproducing wavelength of DVD-R or the like, and arecording or reproducing wavelength is in the vicinity of a longerwavelength end of the above-mentioned absorption band. This means thatthe above-mentioned material for the recording layer has a greaterrefractive index and extinction coefficient within 600-700 nm, which isa recording or reproducing wavelength.

[0065] More particularly, the refractive index “n” of a single layer ofthe recording layer is preferably 1.5-3.0, and the extinctioncoefficient “k” of a single layer of the recording layer is preferablywithin the range of 0.02-0.3, at the wavelength range of the recordingor reproducing wavelength±5 nm in the vicinity of the longer wavelengthend of the above-mentioned absorption band. When “n” is 1.5 or greater,a modulation depth of recording becomes higher, and when “n” is 3.0 orsmaller, an error does not occur with the light in the recording orreproducing wavelength range. In addition, when “k” is 0.02 or greater,the recording sensitivity is improved and, when “k” is 0.3 or smaller,the reflectance of 50% or greater can be easily obtained.

[0066] In addition, the maximum absorption wavelength (λ_(max)) of thematerial for the recording layer which is measured in its solution ispreferably within the range of 550-600 nm, and logε thereat (ε is amolar extinction coefficient) is preferably 5 or bigger.

[0067] In order to evaluate the thermal properties of the aforementionedsquarylium compound, thermogravimetric analysis was performed to observethe loss in weight due to temperature rising. Herein, among someloss-in-weight processes (loss process), one having the greatest degreeof the loss in weight is referred to as a principal loss-in-weightprocess.

[0068] For the thermal properties, it is necessary that the loss inweight in the principal loss-in-weight process is steep relative to atemperature change, because the compound of the present invention isdecomposed in the principal loss-in-weight process, and causes adecrease in a membrane thickness and a change in optical constants and,thereby, a recording portion in an optical sense is formed. Accordingly,when the loss in weight in the principal loss-in-weight process isshelvy relative to the temperature change, it becomes extremelydisadvantageous to form a high density recording portion because therecording portion is formed over a wide temperature range. For thesimilar reason, the material having multiple loss-in-weight processes isalso disadvantageous in application to the high recording density.

[0069] In the present invention, the temperature slope of the loss inweight is calculated as follows.

[0070] As illustrated in FIG. 1, a temperature of the compound of thepresent invention of the weight M0 is risen at a rate of 10° C./min.under the nitrogen atmosphere. As the temperature rises, the weight ofthe compound slightly decreases almost along the straight line a-b, andthe weight steeply decreases almost along the straight line c-d afterreaching the certain temperature. As the temperature further rises, asteep loss in weight is terminated and the loss in weight almost alongthe straight line e-f is caused. In the graph, at an intersection pointof the straight lines a-b and c-d, a temperature is defined as T1 (°C.), and a ratio of the remaining weight relative to the initial weightM0 is defined as m1 (%). In addition, at an intersection point of thestraight lines c-d and e-f, a temperature is defined as T2 (° C.), and aratio of the remaining weight relative to the initial weight M0 isdefined as m2 (%).

[0071] That is, in the principal loss-in-weight process, a weightlosing-initiation temperature is T1, a weight losing-terminationtemperature is T2, and a ratio of the loss in weight is represented by:

[0072] (m1-m2) (%), and

[0073] a temperature slope of the loss in weight is represented by:

[0074] (m1-m2)(%)/(T2-T1)(° C.)

[0075] According to the above definitions, a recording material utilizedfor the optical information recording medium has preferably thetemperature slope of the loss in weight in the principal loss-in-weightprocess of 1% /° C. or greater. When the recording material having thetemperature slope of the loss in weight of 1%/° C. or greater is used, agroove width of the recording portion is not widen, and a shorterrecording portion can be easily formed.

[0076] In addition, the ratio of the loss in weight in the principalloss-in-weight process for the recording material is preferably 20% orgreater. When the ratio of the loss in weight is 20% or greater, itallows a better modulation depth of recording and recording sensitivity.

[0077] Moreover, for the thermal properties, it is necessary that theweight losing-initiation temperature (T1) is within the particulartemperature range. More particularly, the weight losing-initiationtemperature is preferably 350° C. or lower, and more preferably withinthe range of 250-350° C. When the weight losing-initiation temperatureis 350° C. or lower, it is not necessary to raise the power of therecording laser beam, and when it is 250° C. or higher, it is preferablein a recording stability sense.

[0078] The preferable substrate shape is under the condition that atrack pitch is within the range of 0.7-0.8 μm and a groove width at thehalf band width is within the range of 0.20-0.36 μm.

[0079] The substrate usually has a guiding groove having a depth of1,000-2,500 Å. The track pitch is usually 0.7-1.0 μm, but is preferably0.7-0.8 μm for the high recording density application. The groove widthis preferably 0.18-0.36 μm as the half band width. When the groove widthis 0.18 μm or wider, the adequate strength of a tracking error signalcan be easily detected, whereas when it is 0.36 μm or narrower, therecording portion is hardly widened in a traverse direction uponrecording, being preferable.

[0080] 1. The Structure of an Optical Recording Medium

[0081] The optical recording medium of the present invention may beformed into an air-sandwich structure or into a closely adheredstructure which is applied to general recordable discs, or may be formedinto a structure of a recordable optical recording medium such as CD-R,DVD-R, or the like.

[0082] 2. The Required Properties and Embodiments of ConstituentMaterials for Each Layer

[0083] The optical recording medium of the present invention has a basicstructure in which a first substrate and a second substrate are adheredvia a recording layer with an adhesive. The recording layer may be asingle layer of an organic dye layer comprising the compound of thepresent invention, or may be a laminated layer of the organic dye layerand a metal refractive layer for enhancing the reflectance. Between therecording layer and the substrate, an undercoat layer or a protectivelayer may be built-up, or they may be laminated for improving thefunction. Most frequently used structure is the first substrate/theorganic dye layer/the metal refractive layer/the protective layer/theadhesive layer/the second substrate.

[0084] a. Substrate

[0085] The substrate to be used should be transmittable to thewavelength of the laser beam to be used when recording or reproducing isconducted from a substrate side, but it is not necessary for thesubstrate to be transmittable to the wavelength when recording orreproducing is conducted from a recording layer side. As the materialfor the substrate, for example, plastics such as polyester, acrylicresin, polyamide, polycarbonate resin, polyolefin resin, phenolic resin,epoxy resin, polyimide, or the like, glasses, ceramics, metals or thelike may be used. Furthermore, a guiding groove or a guiding pit fortracking, a preformat such as an addressing signal, or the like may beformed on a surface of the substrate.

[0086] b. Recording Layer

[0087] The recording layer is a layer in which some optical change iscaused by irradiation with a laser beam and, thereby, an information isrecorded, and should contain the compound of the present invention. Thecompounds of the present invention may be used alone or in combinationof two or more for forming the recording layer.

[0088] In addition, the compound of the present invention may be used bymixing it or laminating it with other organic dyes, metals or metalcompounds for the purpose of enhancement of the optical properties, therecording sensitivity, the signal properties, or the like. Examples ofthe organic dye include a polymethine dye, naphthalocyanine,phthalocyanine, squarylium, croconium, pyrylium, naphthoquinone,anthraquinone (indanthrene), xanthene, triphenylmethane, azulene,tetrahydrocholine, phenanthrene and triphenothiazine dyes, metal complexcompounds, and the like. Examples of the metal and metal compoundinclude In, Te, Bi, Se, Sb, Ge, Sn, Al, Be, TeO₂, SnO, As, Cd, and thelike, each of which may be used in the form of dispersion mixture orlamination.

[0089] It is possible to enhance the light resistance significantly bymixing a light stabilizer into the compound of the present invention. Asthe light stabilizer, metal complexes and aromatic amines arepreferable. Embodiments of the light stabilizer will be listed below(see Tables 4 and 5).

[0090] The mixing ratio of the light stabilizer relative to the compoundof the present invention is preferably 5-40% by weight. When the ratiois less than 5% by weight, the effect is low, whereas when the ratio isabove 40% by weight, the recording or reproducing properties may beadversely effected in some cases.

[0091] In addition, macromolecular materials, for example, variousmaterials such as ionomer resin, polyamide resin, vinyl resin, naturalpolymer, silicone or liquid rubber, or silane coupling agents may bedispersed and mixed into the compound of the present invention, andadditives such as stabilizers (for example, transition metal complex),dispersing agents, flame retardants, lubricants, antistatic agents,surfactants or plasticizers may be used together for the purpose ofmodifying the properties.

[0092] The recording layer may be formed using conventional methods suchas a deposition, a sputtering, a chemical vapor deposition or a solventcoating. In the case where the coating method is used, the dyecomprising the compound of the present invention optionally with theaforementioned additives added or the like is dissolved in an organicsolvent, and the solution is coated by the conventional coating methodsuch as a spraying, a roller coating, a dipping or a spin coating.

[0093] Examples of the organic solvent to be used generally includealcohols such as methanol, ethanol and iso-propanol, ketones such asacetone, methyl ethyl ketone and cyclohexanone, amides such asN,N-dimethylformamide and N,N-dimethylacetoamide, sulfoxides such asdimethyl sulfoxide, ethers such as tetrahydrofuran, dioxane, diethylether and ethyleneglycol monomethyl ether, esters such as methyl acetateand ethyl acetate, aliphatic halogenated hydrocarbons such aschloroform, methylene chloride, dichloroethane, carbon tetrachloride andtrichloroethane, aromatic compounds such as benzene, xylene,monochlorobenzene and dichlorobenzene, cellosolves such asmethoxyethanol and ethoxyethanol, and hydrocarbons such as hexane,pentane, cyclohexane and methylcyclohexane.

[0094] The membrane thickness of the recording layer is preferably 100Å-10 μm, more preferably 200-2,000 ÅA.

[0095] Embodiments of the light stabilizer to be used in combinationwith the compound of the present invention are shown below.

[0096] (1) Metal complex-light stabilizers (see Table 4)

[0097] wherein R_(a) and R_(b) are the same or different, and representa hydrogen atom, an alkyl group optionally having a substituent, an arylgroup or a heterocyclic group.

[0098] wherein R_(a)R_(b), R_(c) and R_(d) are the same or different,and represent a hydrogen atom, a halogen atom, an alkyl group bondingdirectly or indirectly via a divalent linking group, an aryl group, acyclic alkyl group or a heterocyclic group.

[0099] wherein X represents O, S or CR_(a)R_(b), wherein R_(a) and R_(b)represent CN, COR_(b), COOR_(d), CONR_(e)R_(f), SO₂R_(g), or a group ofatoms necessary for forming a 5- or 6-membered ring, and whereinR_(c)˜R_(g) are the same or different, and represent an alkyl groupoptionally having a substituent or an aryl group.

[0100] wherein R_(a), R_(b), R_(c) and R_(d) are the same or different,and represent a hydrogen atom, a halogen atom, an alkyl group bondingdirectly or indirectly via a divalent linking group, an aryl group, acyclic all group or a heterocyclic group, and R_(e) represents ahydrogen atom, an alkyl group, an aryl group, an acyl group, a carboxylgroup, an alkoxycarbonylalkyl group or a sulfo group.

[0101] wherein R_(a), R_(b), R_(c) and R_(d) are the same or different,and represent a hydrogen atom, a halogen atom, an alkyl group bondingdirectly or indirectly via a divalent linking group, an aryl group, acyclic alkyl group or a heterocyclic group, and R_(e) and R_(f) are thesame or different, and represent a hydrogen atom, an alkyl group, anaryl group, an acyl group, a carboxyl group or a sulfo group.

[0102] wherein X represents O or S, R_(a), R_(b) and R_(c) are the sameor different, and represent an alkyl group optionally having asubstituent bonding directly or via an oxy group, a thio group or anamino group, an aryl group or a cyclic alkyl group, and the symbol:

[0103] C

C

C

[0104] represents C═C—C or C—C═C

[0105] wherein X represents O or S, R_(a), R_(b) and R_(c) are the sameor different, and represent an alkyl group optionally having asubstituent bonding directly or via an oxy group, a thio group or anamino group, an aryl group or a cyclic all group, and R_(d) representsan alkyl group or an aryl group, and the symbol:

[0106] C

C

C

[0107] represents C═C—C or C—C═C.

[0108] wherein R_(a) and R_(b) are the same or different, and representa hydrogen atom, an alkyl group optionally having a substituent, or anaryl group or a heterocyclic group.

[0109] wherein R_(a), R_(b), R_(c) and R_(d) are the same or different,and represent a hydrogen atom, a halogen atom, an alkyl group bondingdirectly or indirectly via a divalent linking group, an aryl group, acyclic alkyl group or a heterocyclic group.

[0110] wherein R_(a), R_(b), R_(c) and R_(d) are the same or different,and represent a hydrogen atom, a halogen atom, an alkyl group bondingdirectly or indirectly via a divalent linking group, an aryl group, acyclic alkyl group or a heterocyclic group, Ft represents a hydrogenatom, an alkyl group, an aryl group, an acyl group, a carboxyl group ora sulfo group.

[0111] In the formulae (A)-(J), M represents a transition metal such asNi, Pd, Pt, Cu, Co, or the like, and may have a charge to form a saltwith a cation, and in addition, other ligands may be bonded above orbelow M. Such salts may be used also as a light stabilizer. The alkyl,cyclic alkyl, aryl and heterocyclic groups and substituents thereforinclude those described above.

[0112] More preferable embodiments are shown in Table 4. TABLE 4Embodiments of metal complex-light stabilizers Metal Corre- Complexsponding Counter Nos. structure R_(a) R_(b) R_(c) R_(d) R_(e) R_(f) X MCation 1 (A) Ph Ph — — — — — Cu NBu₄ 2 (A) C₄H₉ C₄H₉ — — — — — Ni — 3(B) Cl H Cl Cl — — — Ni NBu₄ 4 (B) H OCH₃ H H — — — Cu — 5 (C) — — — — —— O Co NBu₄ 6 (C) — — — — — — S Ni CN 7 (D) H OCH₃ H H CH₂COOEt — — PdNBu₄ 8 (D) H H H H CH₃ — — Ni PBu₄ 9 (D) H CH₃ H H CH₃ — — Pt NPe₄ 10(E) H H H H CH₃ CH₃ — Ni NBu₄ 11 (E) H OCH₃ H H C₂H₅ C₂H₅ — Pt NEt₄ 12(F) H H H — — — O Cu NBu₄ 13 (F) H H H — — — O Ni PBu₄ 14 (F) H Ph H — —— S Ni NOc₄ 15 (G) H H H H — — O Ni NBu₄ 16 (G) H H H H — — S Ni PEt₄ 17(H) Ph Ph — — — — — Pd NBu₄ 18 (I) H H H H — — — Ni NBu₄ 19 (I) H OCH₃ HH — — — Ni PEt₄ 20 (J) H H H H CH₃ — — Ni NBu₄ 21 (J) H H H H C₄H₉ — —Ni PBu₄ 22 (J) H CH₃ H H C₄H₉ — — Cu NOc₄

[0113] 2) Aromatic amine-light stabilizers (see Table 5)

[0114] Following compounds may be used.

[0115] wherein R_(g), R_(b), R_(i) and R_(j) are the same or different,and each represents a hydrogen atom, or an alkyl group optionally havinga substituent, X represents an acid anion, and A is, when m is 1 or 2,

[0116] wherein p is 1 or 2, and is, when m is 2,

[0117] wherein all of existing aromatic rings may be substituted with analkyl group having from 1 to 6 carbon atoms, an alkoxy group having from1 to 6 carbon atoms, a halogen atom or a hydroxyl group.

[0118] More preferred embodiments are shown in Table 5. TABLE 5Embodiments of aminium, imonium and diimonium compounds Com- pound Nos.R_(g) R_(h) R_(i) R_(j) A X m 101 C₂H₅ C₂H₅ C₂H₅ C₂H₅ Z1, p = 2 ClO₄ 1102 C₂H₅ C₂H₅ C₂H₅ C₂H₅ Z1, p = 1 SbF₆ 1 103 C₃H₇ C₃H₇ C₃H₇ C₃H₇ Z1, p =1 Br 1 104 C₃H₇ C₃H₇ C₃H₇ C₃H₇ Z1, p = 2 PF₆ 1 105 C₄H₉ C₄H₉ C₄H₉ C₄H₉Z1, p = 1 ClO₄ 1 106 C₃H₇ H C₃H₇ H Z1, p = 1 ClO₄ 1 107 C₂H₅ C₂H₅ C₂H₅C₂H₅ Z1, p = 2 Cl 1 108 C₆H₁₃ H C₅H₁₃ H Z1, p = 1 SbF₆ 1 109 C₆H₁₃ HC₆H₁₃ H Z1, p = 1 ClO₄ 1 110 C₂H₅ C₂H₅ C₂H₅ C₂H₅ Z1, p = 1 SbF₆ 1 111C₃H₇ C₃H₇ C₃H₇ C₃H₇ Z1, p = 2 ClO₄ 1 112 C₂H₅ C₂H₅ C₂H₅ C₂H₅ Z2 PF₆ 2113 C₂H₅ C₂H₅ C₂H₅ C₂H₅ Z2 ClO₄ 2 114 C₃H₇ C₃H₇ C₃H₇ C₃H₇ Z2 SbF₆ 2 115C₃H₇ H C₃H₇ H Z2 AsF₆ 2 116 C₄H₉ C₄H₉ C₄H₉ C₄H₉ Z2 I 2 117 C₆H₁₃ H C₆H₁₃H Z2 ClO₄ 2

[0119] c. Undercoat Layer

[0120] The undercoat layer is used for the purpose of (1) an improvementof adherability, (2) a barrier against water, gases, or the like, (3) animprovement of the storage stability of the recording layer, (4) anenhancement of the reflectance, (5) a protection of the substrate from asolvent, (6) a formation of a guiding groove, guiding pit or preformat,or the like. With regard to the purpose of (1), macromolecularmaterials, for example, various polymers such as ionomer resin,polyamide resin, vinyl resin, natural resin, natural polymer, silicone,liquid rubber, or the like, silane coupling agents, or the like may beused. With regard to the purposes of (2) and (3), in addition to theaforementioned macromolecular materials, inorganic compounds such asSiO, MgF, SiO₂, TiO, ZnO, TiN, SiN, or the like, and further metals orsemimetals such as Zn, Cu, Ni, Cr, Ge, Se, Au, Ag, Al, or the like maybe used. Moreover, with regard to the purpose of (4), metals such as Al,Au, Ag, or the like, or organic films having metallic luster such as amethine dye, a xanthene dye, or the like may be used. With regard to thepurposes of (5) and (6), a ultraviolet-curing resin, a thermosettingresin, a thermoplastic resin, or the like may be used.

[0121] The membrane thickness of the undercoat layer is preferably0.01-30 μm, more preferably 0.05-10 μm.

[0122] d. Metal Refractive Layer

[0123] Examples of the material for the metal refractive layer includepoorly erodable metals, semimetals, and the like exhibiting a highreflectance themselves. Embodiments of the material for the metalrefractive layer include Au, Ag, Cr. Ni, Al, Fe, Sn, and the like, butAu, Ag and Al are most preferred from a viewpoint of the reflectance andproductivity. These metals or semimetals may be used alone or as analloy of two of them.

[0124] The method for forming a membrane includes a vapor deposition, asputtering, and the like. The membrane thickness of the metal refractivelayer is preferably 50-5,000 Å, more preferably 100-3,000 Å.

[0125] e. Protective Layer, Substrate Surface-hard Coating Layer

[0126] A protective layer and a substrate surface-hard coating layer areused for the purpose of (1) a protection of the recording layer(refraction absorbing layer) from flaw, dust, dirt or the like., (2) animprovement in the storage stability of the recording layer (refractionabsorbing layer), (3) an improvement in the reflectance, or the like.With regard to such purposes, the materials described for the undercoatlayer may be used. In addition, SiO, SiO₂ or the like may be used as aninorganic material, and thermo-softening resins such as polymethylacrylate, polycarbonate, polystyrene, polyester, vinyl resin, cellulose,aliphatic hydrocarbons, natural rubber, styrene-butadiene, chloroprenerubber, wax, alkyd, drying oil, or rosin, thermosetting resins such asepoxy resin, phenol resin, polyurethane resin, melamine resin, or urearesin, or ultraviolet-curing resins such as polyester acrylate, epoxyacrylate, urethane acrylate, or silicone acrylate, or the like may beused as an organic material, but among thern, the ultraviolet-curingresins may be preferably used in that they have the excellentproductivity.

[0127] The membrane thickness of the protective layer or the substratesurface-hard coating layer is preferably 0.01-30 μm, more preferably0.05-10 μm. In the present invention, stabilizers, dispersing agents,flame retardants, lubricants, antistatic agents, surfactants,plasticizers or the like may be incorporated into the above undercoatlayer, protective layer and substrate surface-hard coating layer asdescribed for the recording layer.

[0128] f. Protective Substrate

[0129] A protective substrate should be transmittable to the wavelengthof the laser beam to be used when the laser beam is irradiated from thisprotective substrate side, whereas it may be transmittable or not to thewavelength when it is used as a mere protective plate. The materialswhich may be used for the protective substrate are the same as those forthe substrate, and plastics such as polyester, acrylic resin, polyamide,polycarbonate resin, polyolefin resin, phenol resin, epoxy resin,polyimide, or the like, glasses, ceramics, metals, or the like may beused.

[0130] g. Adhesive, Adhesive Layer

[0131] As the adhesive, any material which can adhere two recordingmedia may be used, but from a viewpoint of the productivity,ultraviolet-curing or hot melt adhesives are preferred.

EXAMPLE

[0132] The following Examples further illustrate the present invention,but are not to be construed to limit the scope of the present invention.

Example 1

[0133] 1.27 g of 3,4-dichloro3-cyclobutene-1,2-dione was dissolved in 20ml of dichioromethane. To this solution, 2.74 g of 3-diethylaminophenolwas added dropwise at 0° C., and the mixture was stirred at 0° C. for 1hour. After the reaction, the precipitate was collected by filtration.The obtained solid was added to a mixture of 6.8 ml of acetic acid and 4ml of water, and the mixture was allowed to react at 110° C. for 3hours. After the reaction was completed, the precipitate was collectedby filtration. To this, 50 ml of n-butanol, 50 ml of toluene and 0.64 gof 2-methyl4-nitroaniline were added, and the mixture was allowed toreact at 110° C. for 8 hours. After the reaction was completed, theprecipitate was collected by filtration to give 0.69 g of thecompound 1. Melting point: 257-258° C.; Elemental analysis (C₂₁H₂₁N₃O₅):Calcd. (%): C, 63.79; H, 5.35; N, 10.63 Found (%): C, 63.67; H, 5.25; N,10.58; IR(KBr) cm⁻¹: 3251, 2973, 1761, 1626, 1381, 1333, 1246, 1223,1190, 1051, 1078; ¹H-NMR δ (CDCl₃) ppm: 1.28 (6H, t, J = 7.1 Hz), 2.50(3H, s), 3.50 (4H, q, J = 7.1 Hz), 6.14 (1H, m), 6.36 (1H, m), 8.05 (1H,m), 8.10 (1H, m), 8.19 (1H, m), 8.41 (1H, m).

Example 2

[0134] In a manner similar to that in Example 1 except that 0.78 g ofcarbazole was used instead of 2-methyl4-nitroaniline, 0.1 g of thecompound 2 was obtained. Melting point: 227° C.; Elemental analysis(C₂₆H₂₂N₂O₃): Calcd. (%): C, 76.08; H, 5.40; N, 6.82 Found (%): C,75.88; H, 5.52; N, 6.84;

Example 3

[0135] 0.87 g of 3,4-dichloro-3-cyclobutene-1,2-dione was dissolved in20 ml of dichloromethane. To this solution, 1.99 g of julolidine wasadded in portions at room temperature, and the mixture was stirred atroom temperature for 4.5 hours. After the reaction, the precipitate wascollected by filtration. The obtained solid was added to 40 ml of aceticacid and 20 ml of water, and the mixture was allowed to react at 110° C.for 4 hours. After the reaction was completed, the precipitate wascollected by filtration. To this, 40 ml of n-butanol, 40 ml of tolueneand 0.78 g of 4-aminoazobenzene were added and the mixture was allowedto react at 110° C. for 1.5 hours. After the reaction was completed, theprecipitate was collected by filtration to give 1.1 g of the compound 3.Melting point: 242-244° C; Elemental analysis (C₂₈H₂₄N₄O₂): Calcd. (%):C, 74.98; H, 5.39; N, 12.49 Found (%): C, 75.16; H, 5.56; N, 12.32; IR(KBr) cm⁻¹: 2856, 1765, 1597, 1500, 1425, 1358, 1304, 1200, 968; H-NMR δ(CDCl₃) ppm: 1.89 (4H, tt, J = 5.6, 5.9 Hz), 2.72 (4H, t, J = 5.9 Hz),3.37 (4H, t, J = 5.6 Hz), 4.91 (1H, m), 7.21 (2H, m), 7.70 (2H, s), 7.95(2H, m), 8.07 (1H, m), 8.16 (2H, m), 8.61 (2H, m).

Example 4

[0136] 1 g of 3,4-dichloro-3-cyclobutene-1,2-dione was dissolved in 11ml of dichloromethane. To this solution, 0.52 g of 8-hydroxyjulolidineand 0.28 g of triethylamine were added in portions at 0° C., and themixture was stirred at 0° C. for 1.5 hours. After the reaction, theprecipitate was collected by filtration. To the obtained solid, 10 ml ofacetic acid and 10 ml of water were added, and the mixture was allowedto react at 110° C. for 2.5 hours. After the reaction was completed, theprecipitate was collected by filtration. To this, 40 ml of n-butanol, 40ml of toluene and 0.27 g of 4-aminoazobenzene were added, and themixture was allowed to react at 110° C. for 1 hour. After the reactionwas completed, the precipitate was collected by filtration to give 0.54g of the compound 4. Melting point: 285-286° C.; Elemental analysis(C₂₈H₂₄N₄O₃): Calcd. (%): C, 72.40; H, 5.21; N, 12.06 Found (%): C,72.27; H, 5.14; N, 11.86; IR (KBr) cm⁻¹: 2935, 1763, 1618, 1597, 1502,1406, 1363, 1342, 1317, 1298, 1228, 1200, 1184, 1153; ¹H-NMR δ (CDCl₃)ppm: 1.85 (4H, m), 2.60 (4H, m), 7.49-7.62 (4H, m), 7.88 (2H, m), 7.94(1H, m), 7.95 (1H, s), 8.01 (2H, m).

Example 5

[0137] In a manner similar to that in Example 4 except that 0.32 g of2-methyl-4-nitroaniline was used instead of 4-aminoazobenzene, 0.48 g ofthe compound 5 was obtained. Melting point: 267° C.; Elemental analysis(C₂₃H₂₁N₃O₅): Calcd. (%): C, 65.86; H, 5.05; N, 10.02 Found (%): C,65.89; H, 4.94; N, 9.95; IR (KBr) cm⁻¹: 3440, 2931, 1765, 1601, 1497,1408, 1365, 1306, 1279, 1225, 1205, 1094; ¹H-NMR δ (CDCl₃) ppm: 1.96(4H, m), 2.48 (3H, s), 2.71 (4H, m), 3.41 (4H, m), 7.66 (1H, s), 8.07(1H, m), 8.17 (2H, m), 8.38 (1H, m).

Example 6

[0138] 0.44 g of 3,4-dichloro-3-cyclobutene-1,2-dione was dissolved in 5ml of dichloromethane. To this solution, 1.00 g of1,3,3-trimethyl-2-methyleneindoline was added dropwise at 4° C., and themixture was stirred at 4° C. for 1.5 hours. After the reaction, theprecipitate was collected by filtration. To the obtained solid, 2.7 mlof concentrated sulfuric acid was added, and the mixture was allowed toreact at 50° C. for 1 hour. After the reaction was completed, thereaction mixture was poured into an excess amount of water, and theinsoluble material was collected by filtration. To this insolublematerial, 10 ml of ethanol, 10 ml of toluene and 0.59 g of4-aminoazobenzene were added, and the mixture was -allowed to react at80° C. for 1 hour. After the reaction was completed, the precipitate wascollected by filtration. The obtained solid was purified by subjectingit to column chromatography (eluent: chloroform/methanol=10/1) to give0.56 g of the compound 6. Melting point: 286° C. (dec.); Elementalanalysis (C₂₈H₂₄N₄O₂): Calcd. (%): C, 74.98; H, 5.39; N, 12.49 Found(%): C, 74.68; H, 5.13; N, 12.42; ¹H-NMR δ (CDCl₃) ppm: 1.70 (6H, s),3.60 (3H, s), 5.80 (1H, s), 7.18- 7.22 (1H, m), 7.37-7.38 (2H, m),7.53-7.63 (3H, m), 7.86-7.89 (2H, m), 7.92-7.94 (2H, m), 8.10-8.13 (1H,m), 11.65 (1H, broad s).

Example 7

[0139] In a maimer similar to that in Example 6 except that 0.34 g of4-amino4′-methoxy-trans-stilbene was used instead of 4-aminoazobenzene,0.35 g of the compound 7 was obtained. Melting point: 293° C. (dec.);Elemental analysis (C₃₀H₂₈N₄O₃): Calcd. (%): C, 78.13; H, 5.92; N, 5.88Found (%): C, 77.92; H, 5.82; N, 5.77; ¹H-NMR δ (CDCl₃) ppm: 1.68 (6H,s), 3.53 (3H, s), 3.78 (3H, m), 5.70 (1H, s), 6.93-6.96 (1H, m), 7.08(1H, d, J = 16.4 Hz), 7.12-7.29 (2H, m), 7.18 (1H, d, J = 16.4 Hz),7.29-7.36 (2H, m), 7.49-7.54 (3H, m), 7.58 (2H, d, J = 8.8 Hz), 7.90(2H, d, J = 8.8 Hz), 11.57 (1H, broad s).

Example 8

[0140] In a manner similar to that in Example 6 except that 0.33 g of4-amino-2-hydroxyazobenzene was used instead of 4-aminoazobenzene andthat purification with column chromatography was not conducted, 0.38 gof the compound 8 was obtained. Melting point: 285° C. (dec.); Elementalanalysis (C₂₈H₂₄N₄O₃): Calcd. (%): C, 72.40; H, 5.21; N, 12.06 Found(%): C, 72.12; H, 4.99; N, 11.93; ¹H-NMR δ (CDCl₃) ppm: 1.71 (6H, s),3.63 (3H, s), 5.83 (1H, s), 7.16- 7.25 (1H, m), 7.37-7.42 (2H, m),7.50-7.59 (5H, m), 7.73 (1H, d, J = 2.2 Hz), 7.80 (1H, d, J = 8.8 Hz),7.93-7.95 (2H, m), 11.53 (1H, broad s), 12.06 (1H, s).

Example 9

[0141] 0.97 g of 3,4-dichloro-3-cyclobutene-1,2-dione was dissolved in10 ml of dichioromethane. To this solution, 2.23 g of1,3,3-trimethyl-2-methyleneindoline was added dropwise at 4° C., and themixture was stirred at 4° C. for 1.5 hours. After the reaction, theprecipitate was collected by filtration. To the obtained solid, 5 ml oftrifluoroacetic acid and 0.07 g of water were added, and the mixture wasallowed to react at 45° C. for 1 hour. After the reaction was completed,the reactant was concentrated with a rotary evaporator. To theconcentrate, acetone was added, and the insoluble material was collectedby filtration. To this insoluble material, 60 ml of n-butanol, 60 ml oftoluene and 0.45 g of 2-aminothiazole were added, and the mixture wasallowed to react at 110° C. for 13.5 hours. After the reaction wascompleted, the precipitate was collected by filtration. The obtainedsolid was purified by subjecting it to column chromatography (eluent:chloroform/methanol=10/1) to give 0.48 g of the compound 9. Meltingpoint: 264-266° C.; Elemental analysis (C₁₉H₁₇N₃O₂S): Calcd. (%): C,64.94; H, 4.88; N, 11.96 Found (%): C, 63.73; H, 4.68; N, 11.71; IR(KBr) cm⁻¹: 3442, 1765, 1612, 1589, 1533, 1498, 1398, 1292, 1234, 1076;¹H-NMR δ (CDCl₃) ppm: 1.72 (6H, s), 3.55 (3H, s), 5.84 (1H, s), 6.79(1H, m), 7.00 (1H, m), 7.16 (1H, m), 7.25 (1H, m), 7.32 (2H, m).

Example 10

[0142] In a manner similar to that in Example 9 except that 0.76 g ofcarbazole was used instead of 2-aminothiazole, 0.67 g of the compound 10was obtained (eluent: chloroform/acetone=10/1). Melting point: 258-258°C.; Elemental analysis (C₂₈H₂₂N₂O₂): Calcd. (%): C, 80.36; H, 5.30; N,6.69 Found (%): C, 80.08; H, 5.14; N, 6.51; IR (KBr) cm⁻¹: 1612, 1579,1570, 1491, 1479, 1446, 1410, 1317, 1290, 1240, 1209, 1111; ¹H-NMR δ(CDCl₃) ppm: 1.86 (6H, s), 3.79 (3H, s), 6.26 (1H, s), 7.10- 7.60 (8H,m), 7.92 (2H, m), 8.96 (2H, m).

Example 11

[0143] 0.78 g of 3,4-dichloro-3-cyclobutene-1,2-dione was dissolved in10 ml of chloroform. To this solution, 1.27 g of1,3,3-trimethyl-2-methylene-5-methoxyindoline was added dropwise at 0°C., and the mixture was stirred at 0° C. for 30 minutes. After thereaction, the precipitate collected by filtration. To the obtainedsolid, 6 ml of trifluoroacetic acid and 1.5 ml of water were added, andthe mixture was allowed to react at 40° C. for 15 minutes. After thereaction was completed, the reactant was concentrated with a rotaryevaporator. To the concentrate, diethyl ether was added, and theinsoluble material was collected by filtration To this insolublematerial, 9 ml of ethanol, 9 ml of toluene and 0.79 g of4-aminoazobenzene were added, and the mixture was allowed to react at80° C. for 1 hour. After the reaction was completed, the precipitate wascollected by filtration. The obtained solid was purified by subjectingit to column chromatography (eluent: chloroform/methanol=10/1) to give0.75 g of the compound 11. Melting point: 280° C. or higher; Elementalanalysis (C₂₉H₂₆N₄O₃): Calcd. (%): C, 72.79; H, 5.48; N, 11.71 Found(%): C, 72.61; H, 5.25; N, 11.59; ¹H-NMR δ (CDCl₃) ppm: 1.76 (6H, s),3.60 (3H, s), 3.80 (3H, m), 5.75 (1H, s), 6.95 (1H, dd, J = 2.4, 8.8Hz), 7.23 (IH, d, J = 2.4 Hz), 7.33 (1H, d, J = 8.8 Hz), 7.52-7.61 (3H,m), 7.86-7.93 (4H, m), 8.08-8.09 (2H, m), 11.42 (1H, broad s).

Example 12

[0144] In a manner similar to that in Example 11 except that 0.45 g of4-amino-2-methoxyazobenzene was used instead of 4-aminoazobenzene andthat purification with column chromatography was not conducted, 0.42 gof the compound 12 was obtained. Melting point: 263° C. (dec.);Elemental analysis (C₃₀H₂₈N₄O₄): Calcd. (%): C, 70.85; H, 5.55; N, 11.02Found (%): C, 70.78; H, 5.37; N, 10.72; ¹H-NMR δ (CDCl₃) ppm: 1.71 (6H,s), 3.61 (3H, s), 3.80 (3H, s), 4.02 (3H, s), 5.78 (1H, s), 6.95 (1H,dd, J = 2.2, 8.8 Hz), 7.23 (1H, d, J = 2.2 Hz), 7.30 (1H, dd, J = 2.2,8.8 Hz), 7.34 (1H, d, J = 8.8 Hz), 7.48-7.59 (2H, m), 7.61 (1H, d, J =8.8 Hz), 7.79-7.82 (2H, m), 8.28 (1H, d, J = 2.2 Hz), 11.36 (1H, broads).

Example 13

[0145] 1.1 g of 3,4-dichloro-3-cyclobutene-1,2-dione was dissolved in 10ml of ethyl acetate. To this solution, 3.25 g of1,1,3-trimethyl-2-methylenebenz[e]indoline was added dropwise at 4° C.,and the mixture was stirred at 4° C. for 2 hours. After the reaction,the precipitate was collected by filtration. To the obtained solid, 19.8g of trifluoroacetic acid and 0.33 g of water were added, and themixture was allowed to react at 45° C. for 3 hours. After the reactionwas completed, the reactant was concentrated with a rotary evaporator.To the concentrate, acetone was added, and the insoluble material wascollected by filtration. To this insoluble material, 20 ml of n-butanol,20 ml of toluene and 0.99 g of 4-aminoazobenzene were added, and themixture was allowed to react at 110° C. for 2 hours. After the reactionwas completed, the precipitate was collected by filtration to give 2.31g of the compound 13. Melting point: 280° C. or higher; Elementalanalysis (C₃₂H₂₆N₄O₂): Calcd. (%): C, 77.09; H, 5.26; N, 11.24 Found(%): C, 77.21; H, 5.39; N, 11.14; IR (KBr) cm⁻¹: 1595, 1583, 1564, 1529,1516, 1410, 1296, 1265, 1248, 1223, 1209.

Example 14

[0146] In a manner similar to that in Example 13 except that 0.72 g of8-aminoquinoline was used instead of 4-aminoazobenzene, 2.06 g of thecompound 14 was obtained. Melting point: 249° C. (dec.); Elementalanalysis (C₂₉H₂₃N₃O₂): Calcd. (%): C, 78.18; H, 5.20; N, 9.43 Found (%):C, 78.22; H, 5.21; N, 9.32; IR (KBr) cm⁻¹: 1610, 1525, 1510, 1497, 1458,1400, 1290, 1261; ¹H-NMR δ (CDCl₃) ppm: 2.07 (6H, s), 3.71 (3H, s), 5.99(1H, s), 7.2- 8.0 (8H, m), 8.1-8.2 (2H, m), 8.4-8.5 (1H, m), 9.0 (1H, d,J = 7.6 Hz), 10.4 (1H, broad s).

Example 15

[0147] In a manner similar to that in Example 13 except that 0.76 g of2-methyl-4-nitroaniline was used instead of 4-aminoazobenzene, 2.06 g ofthe compound 15 was obtained. Melting point: 280° C. or higher (dec.);Elemental analysis (C₂₇H₂₃N₃O₄): Calcd. (%): C, 71.51; H, 5.11; N, 9.27Found (%): C, 71.48; H, 5.04; N, 9.16; IR (KBr) cm⁻¹: 1606, 1591, 1539,1506, 1346, 1281, 1254; ¹H-NMR δ (CDCl₃) ppm: 2.03 (6H, s), 2.49 (3H,s), 3.81 (3H, s), 6.06 (1H, s), 7.3-8.3 (8H, m), 8.50 (1H, d, J = 9 Hz).

Example 16

[0148] In a manner similar to that in Example 13 except that 1 g ofcarbazole was used instead of 4-aminoazobenzene and that columnchromatography (eluent: n-hexane/acetone=10/1) was conducted, 0.22 g ofthe compound 16 was obtained. Melting point: 218-219° C. (dec.);Elemental analysis (C₃₂H₂₄N₂O₂): Calcd. (%): C, 82.03; H, 5.16; N, 5.98Found (%): C, 81.77; H, 5.42; N, 5.64; IR (KBr) cm⁻¹: 1618, 1583, 1566,1491, 1446, 1412, 1286, 1265, 1246, 1221, 1207, 1182; ¹H-NMR δ (CDCl₃)ppm: 2.12 (6H, s), 3.92 (3H, s), 6.32 (1H, s), 7.3- 8.0 (11H, m), 8.20(1H, d, J = 8.5 Hz), 8.96 (2H, d, J = 8.3 Hz).

Example 17

[0149] 1.39 g of 3,4-dichloro-3-cyclobutene-1,2-dione was dissolved in60 ml of methyl-t-butyl ether. To this solution, 5.34 g of1,3di-n-butyl-2-methylene-2,3-dihydroimidazo[4,5-b]quinoxaline was addeddropwise at 4° C., and the mixture was stirred at 4° C. for 2 hours.After the reaction, the precipitate was collected by filtration. To theobtained solid, 6.47 g of trifluoroacetic acid and 0.12 g of water wereadded, and the mixture was allowed to react at 45° C. for 4 hours. Afterthe reaction was completed, the reactant was concentrated with a rotaryevaporator. To the concentrate, acetone was added, and the insolublematerial was collected by filtration. To this insoluble material, 15 mlof n-butanol, 15 ml of toluene and 0.4 g of 1,2,3,4-tetrahydroquinolinewere added, and the mixture was allowed to react at 110° C. for 2 hours.After the reaction was completed, the precipitate was collected byfiltration, and the obtained solid was purified by subjecting it tocolumn chromatography (eluent: chloroform/acetone=15/1) to give 0.97 gof the compound 17. Melting point: 211-212° C.; Elemental analysis(C₃₁H₃₅N₅O₂): Calcd. (%): C, 73.35; H, 6.55; N, 13.80 Found (%): C,73.05; H, 6.49; N, 13.92; IR (KBr) cm⁻¹: 1620, 1589, 1510, 1481, 1464,1452, 1396, 1336, 1325, 1300, 1273, 1178, 1122; ¹H-NMR δ (CDCl₃) ppm:0.95 (6H, t, J = 7.3 Hz), 1.30-1.40 (4H, m), 1.70-1.9 (4H, m), 2.16 (2H,m), 2.95 (2H, t, J = 6.7 Hz), 4.53 (2H, t, J = 5.6 Hz), 4.67 (4H, t, J =7.3 Hz), 5.55 (1H, s), 7.1-8.0 (8H, m).

Example 18

[0150] In a manner similar to that in Example 17 except that 0.29 g of3-aminopyridine was used instead of 1,2,3,4-tetrahydroquinoline, 0.74 gof the compound 18 was obtained (eluent: chloroform/methanol=15/1).Melting point: 259-260° C.; Elemental analysis (C₂₇H₂₃N₆O₂): Calcd. (%):C, 69.21; H, 6.02; N, 17.94 Found (%): C, 68.98; H, 6.01; N, 17.73; IR(KBr) cm⁻¹: 1614, 1576, 1537, 1504, 1481, 1392, 1319, 1184, 1124; ¹H-NMRδ (CDCl₃) ppm: 0.95 (6H, t, J = 7.5 Hz), 1.3-1.4 (4H, m), 1.80- 1.9 (4H,m), 4.76 (4H, t, J = 7.3 Hz), 5.69 (1H, s), 7.33 (1H, m), 7.67 (2H, m),8.06 (2H, m), 8.35 (1H, m), 8.68 (1H, m), 8.98 (1H, d, J = 2.2 Hz), 10.5(1H, broad s).

Example 19

[0151] In a manner similar to that in Example 17 except that 0.44 g of3-aminoquinoline was used instead of 1,2,3,4-tetrahydroquinoline andthat purification with column chromatography was not conducted, 0.76 gof the compound 19 was obtained. Melting point: 266° C. (dec.);Elemental analysis (C₃₁H₃₀N₆O₂): Calcd. (%): C, 71.79; H, 5.83; N, 16.20Found (%): C, 71.75; H, 5.63; N, 16.05; IR (KBr) cm⁻¹: 1624, 1593, 1574,1549, 1504, 1473, 1462, 1394, 1317, 1182, 1122; ¹H-NMR δ (CDCl₃) ppm:0.95 (6H, t, J = 7.5 Hz), 1.30-1.50 (4H, m), 1.8-1.9 (4H, m), 4.78 (4H,t, J = 7.5 Hz), 7.0 (1H, s), 7.4-8.1 (8H, m), 9.0 (1H, d, J = 2.2 Hz),9.2 (1H, d, J = 2.7 Hz).

Example 20

[0152] In a manner similar to that in Example 17 except that 0.44 g of8-aminoquinoline was used instead of 1,2,3,4-tetrahydroquinoline andthat purification with column chromatography was not conducted, 0.48 gof the compound 20 was obtained. Melting point: 233° C. (dec.);Elemental analysis (C₃₁H₃ON₆O₂): Calcd. (%): C, 71.79; H, 5.83; N, 16.20Found (%): C, 71.51; H, 5.79; N, 15.90; IR (KBr) cm⁻¹: 1630, 1618, 1516,1500, 1483, 1392, 1311, 1184, 1126, 1086; ¹H-NMR δ (CDCl₃) ppm: 0.96(6H, t, J = 7.3 Hz), 1.30-1.50 (4H, m), 1.8-1.9 (4H, m), 4.77 (4H, t, J= 7.3 Hz), 5.73 (1H, s), 7.4-7.7 (5H, m), 8.0 (2H, m), 8.16 (1H, m),.8.8 (1H, m), 8.95 (1H, m), 10.3 (1H, broad s).

Example 21

[0153] The maximum absorption wavelength (λ_(max)) and the log ε (ε is amolar extinction coefficient) at the maximun absorption wavelength for asolution of the compound prepared in Example 1, 2, 7, 8, 10, 13, 15 or17 in chloroform were measured. The results are shown in Table 6.

Example 22

[0154] T1, T2, (m1-m2)(%)/(T2-T1)(° C.) and (m1-m2)(%) for the compoundsprepared in Examples 1, 2, 7, 8, 10, 13, 15 and 17 measured with TG-DTA(a thermogravimetric-differential thermal analyzer) are shown in Table6.

Comparative Example

[0155] The spectroscopic (maximum absorbing wavelength and molarextinction coefficient) and thermal decomposition properties (weightlosing-initiation temperature, weight losing-termination temperature,ratio of the loss in weight, and temperature slope of the loss inweight) which were measured for the squarylium compound represented bythe following formula (a) (Japanese Unexamined Patent Publication No.92914/1994) in a manner similar to those in Examples 21 and 22 are shownin Table 6. TABLE 6 (a)

Spectroscopic and thermal decomposition properties of squaryliumcompounds Spectroscopic properties (chloroform solution) Thermaldecomposition properties Compounds $\begin{matrix}\lambda_{\max} \\({nm})\end{matrix}\quad$

logε $\begin{matrix}{T1} \\\left( {{^\circ}\quad {C.}} \right)\end{matrix}\quad$

${\begin{matrix}{T2} \\\left( {{^\circ}\quad {C.}} \right)\end{matrix}\quad}\quad$

$\frac{\left( {{m1} - {m2}} \right)\quad (\%)}{\left( {{T2} - {T1}} \right)\quad \left( {{^\circ}\quad {C.}} \right)}$

$\begin{matrix}\left( {{m1} - {m2}} \right) \\(\%)\end{matrix}\quad$

1 550.5 5.1 269.3 283.6 1.5 21.3 2 569.0 5.2 250.6 262.3 1.9 22.5 7551.0 5.0 307.0 317.0 2.3 22.7 8 572.0 5.2 302.0 317.0 1.8 26.7 10 567.05.1 277.5 290.4 1.7 21.7 13 574.0 5.1 346.7 368.0 1.5 32.1 15 567.5 5.1312.3 336.1 1.1 25.2 17 576.0 5.0 292.1 310.6 1.6 30.4 ComparativeExamples a 568.0 4.7 255.3 264.7 1.5 14.1

[0156] Examples relating to the optical recording media will beillustrated below.

Example 23

[0157] A solution prepared by dissolving the compound 1 in2,2,3,3-tetrafluoro-1-propanol was spinner-coated on an injectionmolded-polycarbonate substrate of 0.6 mm thickness having a guidinggroove of the groove depth of 1,750 Å, the half band width of 0.25 μm,and the track pitch of 0.74 μm to form an organic dye layer having athickness of 900 Å. The optical constants of the resulting recordingmembrane are shown in Table 7. In the table, n represents a refractiveindex of the single layer of the recording layer, and k represents anextinction coefficient.

[0158] Then, a gold refractive layer having a thickness of 1,200 Å wasprovided thereon by a sputtering method, the protective layer having athickness of 7 μm was further provided thereon with an acrylicphotopolymer, and then an injection molded-polycarbonate flat substratehaving a thickness of 0.6 mm was adhered thereto with an acrylicphotopolymer to prepare a recording medium.

[0159] An EFM signal was recorded on the prepared recording medium withtracking (linear speed of 3.5 m/sec.) using the semiconductor laser beamhaving an oscillation wavelength of 650 nm and a beam diameter of 1.0μm, and then the recorded signal was reproduced with a continuous beamof the semiconductor laser having an oscillation wavelength of 650 nm(reproduction power of 0.7 mW). The resulting signal properties areshown in Table 8.

Examples 24-28

[0160] The recording membrane was formed in a manner completely similarto that in Example 23 except that the compound 10, 11, 14, 16 or 18 wasused instead of the compound 2 (Examples 24-28). The optical constantsof the resulting recording membrane are shown in Table 7. Furthermore,the recording medium was formed in a manner completely similar to thatin Example 23 and the signal properties thereof were measured. Theresulting signal properties are shown in Table 8. TABLE 7 Opticalconstants of recording membrane λ = 635 nm λ = 650 nm n k n k Compound 22.54 0.30 2.66 0.13 Compound 10 2.61 0.10 2.40 0.05 Compound 11 2.910.32 2.67 0.10 Compound 14 2.55 0.03 2.39 0.02 Compound 16 2.66 0.222.41 0.05 Compound 18 3.04 0.49 2.77 0.12

[0161] TABLE 8 Signal properties of recording medium Reflectance (%):Modulation depth (%): flat portion I₁₁/I_(top) Jitter (%) Example 2365.2 61.7 8.8 (Compound 2) Example 24 63.7 62.8 9.0 (Compound 10)Example 25 65.5 61.5 8.6 (Compound 11) Example 26 63.3 63.2 8.9(Compound 14) Example 27 63.8 62.4 9.1 (Compound 16) Example 28 65.760.8 8.7 (Compound 18)

Example 29

[0162] A recording medium was formed, using a mixture of the compound 2and the metal complex No. 3 (see Table 4; weight ratio of compound2/metal complex No. 3=10/3) instead of the compound 2 in Example 23.

[0163] A light from a xenon lamp (50,000 luxes) was irradiated on thisrecording medium for 10 hours, and a remaining ratio of an opticaldensity was evaluated. The remaining ratio of an optical density wascalculated by the following equation:

Remaining ratio of an optical density=I_(d)/I_(o)×100(%)

[0164] I_(d): Optical density after irradiation;

[0165] I_(o): Optical density before irradiation.

[0166] The results of the light resistance test are shown in Table 9.

Examples 30-32

[0167] The recording layer was formed using the aromatic amine compoundNo. 104 (see Table 5) instead of the metal complex No. 3 (Example 30),and further using a mixture of the compound 11 and the metal complex No.12 (see Table 4) instead of a mixture of the compound 2 and the metalcomplex No. 3 (Example 31), or a mixture of the compound 11 and thearomatic amine compound No. 113 (see Table 4) instead of a mixture ofthe compound 2 and the metal complex No. 3 (Example 32) in Example 29. Alight resistance test was performed on the resulting recording layer ina manner similar to that in Example 29. The results of the lightresistance test are shown in Table 9. TABLE 9 Results of lightresistance test of recording layer Compound Light stabilizer Remainingratio of Nos. Nos. Optical density (%) Example 23  2 — 22 Example 25 11— 28 Example 29  2  3 88 Example 30  2 104 92 Example 31 11  12 90Example 32 11 113 93

Industrial Applicability

[0168] According to the present invention, there can be providedsquarylium compounds having spectroscopic and thermal decompositionproperties suitable for an oscillation wavelength of a semiconductorlaser utilized for a digital versatile disc-recordable (DVD-R). Also,DVD-R media having the excellent light resistance as well as the highreflectance and modulation depth can be provided by using the squaryliumcompound prepared by the present invention as a recording material.

What is claimed is:
 1. A squarylium compound represented by the generalformula (I):

wherein, R¹ and R² are the same or different, and represents a hydrogenatom, an alkyl group optionally having a substituent, an aralkyl groupoptionally having a substituent, an aryl group optionally having asubstituent or a heterocyclic group optionally having a substituent, orR¹ and R² may be taken together with an adjacent nitrogen atom to form aheterocycle, wherein the heterocycle may have a substituent; and R³represents the general formula (II):

wherein, R⁴ and R⁵ are the same or different, and represent a hydrogenatom or an alkyl group, or R⁴ and R⁵ may be taken together with anadjacent nitrogen atom to form a heterocycle; and R⁶, R⁷, R⁸ and R⁹ arethe same or different, and represent a hydrogen atom, an alkyl groupoptionally having a substituent or an alkoxy group optionally having asubstituent, a hydroxyl group or a halogen atom, or R⁴ and R⁶ or R⁵ andR⁷ may be taken together with adjacent N—C—C to form a heterocycle,wherein the heterocycle may have a substituent; or the general formula(III):

wherein, R¹⁰ represents a carbon or nitrogen atom; R¹¹ and R¹² are thesame or different, and represent a hydrogen atom, an alkyl groupoptionally having a substituent, an aryl group optionally having asubstituent, an aralkyl group optionally having a substituent or ahydroxyl group (provided that, when R¹⁰ is a nitrogen atom, then R¹² isnot present); R¹³ represents a hydrogen atom, an alkyl group optionallyhaving a substituent, an aryl group optionally having a substituent oran aralkyl group optionally having a substituent; and R¹⁴ and R¹⁵ arethe same or different, and represent a hydrogen atom, an alkyl groupoptionally having a substituent, an alkoxy group or a halogen atom, orR¹⁴ and R¹⁵ may be taken together with two adjacent carbon atoms to forman alicyclic hydrocarbon ring, an aromatic ring optionally having asubstituent or a heterocycle optionally having a substituent.
 2. Anoptical recording medium, which comprises a recording layer containingthe squarylium compound represented by the general formula (I) accordingto claim
 1. 3. The optical recording medium according to claim 2,wherein the recording layer contains a light stabilizer.
 4. The opticalrecording medium according to claim 3, wherein the light stabilizer isselected from the group consisting of a metal complex and an aromaticamine.
 5. The optical recording medium according to claim 4, whichcontains 5-40% by weight of the light stabilizer relative to thesquarylium compound.
 6. The optical recording medium according to anyone of claims 2-5, wherein a single layer of the recording layer has therefractive index (n) of 1.5≦n≦3.0 and the extinction coefficient (k) of0.02≦k≦0.3 for the light of a wavelength range of a recording orreproducing wavelength±5 nm.
 7. The optical recording medium accordingto any one of claims 2-6, wherein the squarylium compound of claim 1 hasa temperature slope of the loss in weight in a principal loss-in-weightprocess in a thermogravimetric analysis of 1%/° C. or greater.
 8. Theoptical recording medium according to any one of claims 2-7, wherein thesquarylium compound of claim 1 has a ratio of the loss in weight in theprincipal loss-in-weight process in a thermogravimetric analysis of 20%or greater and a weight losing-initiation temperature of 350° C. orlower.
 9. The optical recording medium according to any one of claims2-8, which has a track pitch on a substrate within the range of 0.7-0.8μm and a groove width at a half band width within the range of 0.20-0.36μm.
 10. The optical recording medium according to any one of claims 2-9,which has a recording or reproducing wavelength within the range of600-700 nm.
 11. The optical recording medium according to any one ofclaims 2-10, which has a maximum absorbing wavelength within the rangeof 550-600 nm and a log ε (ε is a molar extinction coefficient) at saidmaximum absorbing wavelength of 5 or bigger.
 12. The squarylium compoundaccording to claim 1, wherein R¹ and R² in the general formula (I) aretaken together with an adjacent nitrogen atom to form a carbazole ringoptionally having a substituent.
 13. The squarylium compound accordingto claim 1, wherein, in the general formula (I), R¹ is a hydrogen atomand R² is —R¹⁶=R¹⁷—Ar (R¹⁶ and R¹⁷ are the same, and represent N or CH,and Ar represents an aryl group optionally substituted with asubstituent selected from the group consisting of a hydroxyl group, acarboxyl group, a nitro group, an alkoxy group, an alkyl groupoptionally substituted with a halogen group, a cyano group and a halogenatom).
 14. The squarylium compound according to claim 12, wherein R³ isa group represented by the general formula (III).
 15. The squaryliumcompound according to claim 13, wherein R³ is a group represented by thegeneral formula (III).
 16. An optical recording medium, which comprisesa recording layer containing the squarylium compound according to anyone of claims 12-15.
 17. The optical recording medium according to claim16, wherein the recording layer contains a light stabilizer.